Gonadotropin releasing hormone (GnRH), both types I and II, is a decapeptide hormone that stimulates the release of gonadotropin, luteinizing hormone (LH) and follicle stimulating hormone (FSH) from the anterior pituitary through specific binding to the GnRH receptor (GnRHR) located on the external membrane of selected cell types. Subsequent studies revealed that GnRH and its receptor also play extra-pituitary roles in numerous normal and malignant cells or tissues, the mechanisms of which are still being actively explored. Lee, G-C. Y., et al., Am J Reprod Immunol (2000) 44:170-177, Chien, C. H., et al., Int J Gynecol Cancer (2004) 14:451-458. Anti-proliferative effects of GnRH or its analogs on cancer cells of different human tissue origins have been reported. (Pati, D., et al., Endocrin (1995) 136:75-84; Choi, K. C., et al., J Clin Endocrinol & Metab (2001) 86:5075-5078.)
Numerous clinical studies have also reported the use of cytotoxic GnRH analogs or GnRH analogs alone as anti-cancer drugs. To improve efficacy, GnRH analogs are sometimes formulated by covalently linking cytotoxic anti-cancer agents, such as AN-152 or AN-207, to GnRH or its analogs. GnRH agonists or antagonists have been reported to suppress cancer cell growth clinically. GnRH analogs, such as Leuprorelin, Buserelin and Goserelin, have been used in the treatment of hormone-responsive cancers, such as prostate and breast cancers. (Gnananpragasam, V. J., et al., J Pathol (2005) 206:205-213; So, W. K., et al., FEBS Journal (2008) 275:5496-5511.) However, limited and variable efficacy was observed in many cases. Nevertheless, this approach has been shown to be effective in cancer treatments with lower toxicity and improved efficacy when compared to non-targeted systemic chemotherapy. (Nagy, A., et al., Biol of Reprod (2005) 73:851-859.)
GnRH analogs have also been used for the treatment of other estrogen-dependent conditions, such as endometriosis, uterine fibroids, and endometrial thinning, to treat precocious puberty, and to control ovarian stimulation in In Vitro Fertilization (IVF).
While it has been established that GnRH and its analogs exhibit antiproliferative effects on cancer cells or tissues, the efficacy of GnRH and its analogs is limited by the relatively short half life in circulation. For example, GnRH has a half life of only 2-4 minutes, while decapeptide GnRH analogs have half-lives of a few hours. Therefore, the use of GnRH or its analogs as drugs generally requires frequent administration. There remains a need for the development of alternate approaches for the treatment of these conditions, using agents having improved half-lives, efficacy and/or tolerability.
The development of antibody-based anti-cancer drugs as an alternative to traditional agents in human cancer treatments has been explored in recent years. It is important that the drug target on the cancer cell surface be clearly identified, expressed with high abundance and its mechanisms of action be well elucidated.
Monoclonal antibodies generally have a relatively long half life in human circulation, typically ranging from about 5 days to 22 days. Thus, the use of monoclonal antibodies as drugs provides an attractive alternative for the treatment of cancer, and antibodies targeting the GnRH receptor provides a major advantage over the decapeptide GnRH analogs due to the much longer half life in circulation (e.g., from 5 days to 22 days versus hours for the peptidic GnRH analogs). In particular, monoclonal antibodies to the GnRH receptor may be useful for the treatment of hormone sensitive cancers, such as prostate and breast cancers, and for the regulation of fertility. Such antibodies may also have a reduced potential for side effects.
A monoclonal antibody against a synthetic peptide corresponding to amino acids 1-29 of the N-terminal extracellular domain of the human GnRH receptor has been reported to bind to a human breast carcinoma and an ovarian carcinoma cell line. Karande, A., et al., Mol. Cell Endocrin. (1995) 114:51-56; Rajeshwari, K. & Karande, A., Immunol. Invest. (1999) 28:103-14. A monoclonal antibody against a synthetic peptide corresponding to amino acids 5-17 of the N-terminal extracellular domain of the mouse hypophyseal GnRH receptor has been reported to react with a human ovarian cancer cell line and to inhibit endometrial maturation in mice. Ackerman, R. C., et al., Cancer Lett. (1994) 81:177-84; Asirvatham, A. L., et al., Am. J. Reprod. Immunol. (1994) 32:95-100.
The generation of anti-GnRH receptor antibodies for the diagnosis and treatment of reproductive disorders and for contraception is disclosed in U.S. Pat. No. 5,750,366. The generation of antibodies to the type II receptor for contraception is also disclosed in US 2003/0124585, as is the use of such antibodies in the treatment of cancer. US 2006/0193853 may suggest the use of anti-GnRH receptor antibodies among many other entities in combination with a growth regulating factor for the treatment of cancer. US 2005/0158309 discloses anti-GnRH receptor antibodies among many other candidates for the treatment of T-cell related neoplastic diseases. US 2003/144203 suggests, among many other candidates, raising antibodies to GnRHR to delay senescence. US 2006/0148697 discloses (again, among many other alternatives) the use of a vaccine or antibody to stimulate the production of antibodies that block the GnRH-receptor as potentially useful for the treatment of brain cancer. None of these documents discloses the preparation of monoclonal antibodies or isolated antibody preparation useful in such treatments.